A Plug for integrating Snarkey ZKP authentication into Plug-based apps.

Usage

plug Snarkey.Plug,
  param_key: "proof",
  lookup: &MyApp.Accounts.get_by_blind_id/1,
  fallback_handler: {MyApp.FallbackController, :challenge}

Expects proof params under conn.body_params[param_key] containing "r", "s", and optionally "timestamp". The :lookup function receives blind_identifier and must return %{public_y: binary()} or nil.

Proof values ("r", "s", "timestamp") are expected as decimal strings and are converted to raw binary-encoded integers before calling Snarkey.authenticate/3.

On success, assigns :snarkey_auth => {:ok, :authenticated} to conn.assigns. On fallback, invokes the fallback handler with conn and the challenge, or assigns :snarkey_auth => {:fallback, challenge} if no handler is configured. On error, returns a 401 response.